As of July 1, all people who want to buy beer in Tennessee must present identification—even if they're clearly senior citizens. "It's the stupidest law I ever heard of. …You can see I'm over 21," one irritated beer drinker in his 60s said to the Associated Press. The new policy is supposed to take the guesswork out of the equation for clerks who aren't always sure if they need to request proof of age. But are we really that terrible at telling how old someone is?
Yes. Researchers have examined the topic of store clerk's accuracy in age estimation, mostly with regard to tobacco and alcohol sales. Clerks and bartenders tend to get more accurate as they spend more time on the job, but they're far from perfect. A 2001 study, for example, found that British bartenders might as well be picking at random when they try to distinguish between girls who are 16 and those who are above the drinking age of 18.
Some people are better than others at guessing ages. Practice helps, so experienced bartenders (and some carnies) tend to be quite adept. For new clerks or those who need some boning up, training—for instance, by displaying pictures of people, asking neophytes to guess the person's age, and then providing feedback on whether they were right or wrong—can help increase a checkout boy's ability to tell a 25-year-old from an 18-year-old. (The Tennessee law encourages stores to train their clerks in "methods of recognizing and dealing with underage customers.")
Our accuracy at guessing someone's age depends on other factors, too. Some research suggests that clerks tend to underestimate the ages of people under 21 and overestimate for people older, while other studies find the opposite. We do best when we're attempting to peg the age of someone who is close to us in age and comes from the same racial background. And we're especially prone to overestimating the ages of teenage girls. In the British study, bartenders were shown pictures of people aged 13 through 22 and asked to guess their ages. They judged about one of every five 13-year-old girls to be over 18, while they correctly identified the 13-year-old boys 97 percent of the time.
The new law might be helpful for any Tennessean store clerks suffering from a disorder called prosopagnosia, or "face blindness." Prosopagnosia, which is sometimes associated with a stroke, autism, brain damage, or other neurological disorder, can limit an individual's ability to estimate age at all.
Got a question about today's news? Ask the Explainer.
Explainer thanks Matthew Rhodes of Colorado State University.